Discogenic pain is a form of back pain arising from one or more intervertebral discs in the spine. Discogenic pain occurs when there is a structural abnormality in an intervertebral disc, such as degeneration, a tear or herniation. In disc degeneration, fluid from the outer fibrous annulus surrounding an intervertebral disc is lost, causing the disc to become brittle. When the disc becomes so brittle that it cracks, the disc releases chemicals that may be a source of discogenic pain. Discogenic pain is also associated with activities that increase the pressure within the intervertebral disc, i.e., the intradiscal pressure. Sitting, bending forward, coughing and sneezing can increase the intradiscal pressure and lead to discogenic pain. In some cases, disc degeneration is chronic, resulting in a condition known as Degenerative Disc Disease.
To diagnose and treat discogenic pain, it is important to accurately locate the source of pain. Currently, discography is the most common way of diagnosing discogenic pain. During discography, a needle is inserted into an intervertebral disc suspected of causing the back pain and a contrast medium is injected into the disc through the needle. Using fluoroscopy, the physician can determine whether the contrast medium is properly positioned within the nucleus of the disc to get an idea about the health of the disc. If the disc is healthy, the contrast medium will stay in the nucleus. If the disc is damaged or degenerated, the contrast medium can spread easily throughout the disc. If the disc is ruptured, the contrast medium can actually discharge out of the nucleus. In addition, the injection of the contrast medium into the disc may cause pain, due to the chemical composition of the contrast medium and/or the increased pressure in the disc upon injection. During the procedure, the patient may be asked to respond if any pain is experienced, especially pain that mimics the condition that the patient is complaining of. Through a combination of subjective analysis of radiographs and a subjective description of the pain reported by the patient, the physician attempts to determine whether the particular disc is causing the patient's pain. In this type of discography procedure, the patient generally remains immobilized.
Despite the widespread use of discography, there are some drawbacks. Some clinicians theorize that if a discogram is positive according to commonly used criteria, then the tested disc is the source of the patient's pain. However, there is no universally accepted definition of the criteria for a positive discogram. As a result, interpretation of discograms is somewhat controversial. Not only does the test rely on subjective feedback, but results themselves have been shown to have a high rate of false positives and false negatives, with a significant number of patients with no back pain having positive discograms. Similarly, some patients have reported feeling a replication of their usual pain during discography, even though it is later found that another, non-discogenic cause was the actual origin of the pain. Moreover, discography is not a particularly selective technique in that it cannot necessarily target a particular portion of the intervertebral disc that is damaged and causing a subject's pain.
In another method of diagnosing and treating discogenic pain, a catheter is inserted into an intervertebral disc. The subject may assume a position that causes the discogenic pain and an anesthetic or analgesic is injected into the disc. The patient is then asked to report whether or not the injected substance has allievated the pain. However, like the conventional disography procedure described above, this method relies on subjective feedback and is not particularly selective. In addition, this method provides only limited data, i.e., the presence or absence of pain.